Adhesive composition and method for preparing same

ABSTRACT

Provided is an adhesive composition including lysine, citric acid, and water, wherein the lysine and the citric acid are present in the form of an aqueous solution of a salt such that precipitates are not formed in the aqueous solution. In addition, provided is a method of preparing an adhesive composition including mixing lysine, citric acid, and water to thereby form a mixture of the lysine, the citric acid, and the water, and stirring the mixture at a temperature of 80° C. or less, wherein amounts of the lysine, the citric acid, and the water are adjusted such that precipitates of the lysine and the citric acid do not form in the adhesive composition.

BACKGROUND 1. Field

One or more embodiments relate to an adhesive composition and a methodof preparing the same.

2. Description of the Related Art

In general, adhesives include a petroleum-derived monomer and anoil-based solvent as raw materials. Monomers made from petroleum-derivedraw materials and adhesives made from such monomers may have problemssuch as decreases in production due to limited oil reserves, generationof endocrine-disrupting chemicals during production of the monomers andadhesives, and toxicity caused by disposal of the monomers andadhesives. In particular, since organic solvents derived from petroleumare used during manufacturing processes of conventional adhesives inorder to improve the adhesive strength of the manufactured adhesives,the health of workers is threatened and there is growing concern aboutenvironmental pollution. In addition, since most of the adhesivesinclude monomer units covalently bonded to each other, naturaldecomposition of the adhesives is difficult and undecomposed polymersmay cause environmental pollution. Therefore, for the efficient removalof adhesives from adherends, various water-removable adhesives have beendeveloped. In order to efficiently remove conventional water-removableadhesives from adherends and substrates, high-temperature and alkalineconditions are required, and additional energy needs to be consumed. Inaddition, secondary environmental pollution may be caused by thedisposal of raw material molecules of the adhesives when the adhesivesattached to adherends or substrates are removed by water.

SUMMARY

An aspect provides an adhesive composition.

Another aspect provides a method of preparing the adhesive composition.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a graph illustrating ¹H nuclear magnetic resonance (NMR)analysis results, according to Example 7;

FIG. 2 is a graph illustrating evaluation results of contact angles withglass, stainless steel (SUS), and polyethylene (PE) substrates,according to Example 10;

FIG. 3 shows a photograph of adhesive compositions applied to substratesand dried at room temperature (25° C.), according to Example 3; and

FIG. 4 shows photographs of adhesive compositions applied to substratesand dried in an oven (40° C.), according to Example 3.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

Hereinafter, an adhesive composition according to an embodiment and amethod of preparing the same will be described in detail.

An adhesive composition including lysine, citric acid, and water,wherein the lysine and citric acid are present in the form of an aqueoussolution of a salt and do not form precipitates in the aqueous solutionis provided.

Throughout the specification, the term “adhesion” refers to a phenomenonin which two objects (except for gases) are close to each other and aforce (or work) is required to separate the two objects by pullingthereafter. If required, some materials having adhesion may besolidified after a given period of time after being applied to asubstrate. When such an adhesive is separated from the substrate,irreversible physical destruction may occur. In addition, the term“adhesion” may include “viscoelasticity” which requires a force onviscoelastic deformation when the adhesive material is separated fromthe substrate. An adhesive composition having viscoelastic propertiesmay be stored and distributed after pretreatment before being applied tothe substrate. Thus, adhesive forces thereof may be maintained after acertain period of time. Examples of adhesive articles prepared byapplying the adhesive composition to a substrate and drying thecomposition may include labels and oriented polypropylene (OPP) tapes.By using the adhesive properties, reversible attachment and detachmentmay be possible. By applying the adhesive composition to the substrateand drying the composition, an adhesive layer having viscoelasticity isformed on the substrate.

Meanwhile, viscosity refers to a property of inhibiting a flow of asubstance caused by internal friction between molecules. In this case,friction is a force to prevent a difference in the distribution of flowvelocities. Adhesion and viscosity are independent properties. Acomposition having a high viscosity may have a very low adhesion and acomposition having a low viscosity may have a high adhesion.

Throughout the specification, the precipitates may include awater-insoluble salt AB(s) obtained by a chemical change of an aqueoussolution of lysine A(aq) and an aqueous solution of itaconic acid B(aq)as shown in Reaction Scheme 1 below, a solid of lysine or itaconic acidA(s) precipitated from an aqueous solution of lysine or itaconic acidA(aq) as shown in Reaction Scheme 2 below, and a solid of lysine oritaconic acid A(s) not dissolved in a solvent but remaining in aninsoluble state.

A(aq)+B(aq)−>AB(s)  Reaction Scheme 1

A(aq)−>A(s)  Reaction Scheme 2

Also, the “precipitates” used herein may refer to precipitates formedselected from before the adhesive composition being applied to thesubstrate or adherend, during storage of the adhesive composition, anddistribution of the adhesive composition.

As used herein, the term “lysine” refers to a basic α-amino acid andlysine may be biosynthesized from oxlaloacetic acid via a lysinebiosynthetic pathway or chemically synthesized.

Lysine may include one type of lysine or a mixture of at least two typesof lysine.

Lysine may include at least one of L-lysine represented by Formula 1below, D-lysine represented by Formula 2 below, and salts thereof.

The lysine salts may include, for example, lysine sulfate, lysineacetate, lysine monohydrochloride, lysine dihydrochloride, lysinemonohydrate, lysine acetylsalicylate, lysine phosphate, lysinediphosphate, a mixture thereof, or a combination thereof. These lysinesalts may be converted into lysine free forms.

Methods of converting lysine salts into lysine free forms are well knownin the art. Also, commercially available lysine raw materials may beused. For example, the lysine may be D-lysine, L-lysine, and/orDL-lysine. Since physicochemical properties thereof are the same orsimilar, characteristics of adhesive compositions including the same arealso the same or similar, and thus they may be included in the scope ofthe present disclosure.

Citric acid is an organic acid represented by Formula 3 below.

In the adhesive composition, lysine and citric acid may be present inthe form of an aqueous solution of a salt. Specifically, althoughlysine, citric acid, and water are mixed, lysine and citric acid may bepresent in the form of an aqueous solution of a salt without forming acovalent compound or an insoluble salt.

In the adhesive composition according to an embodiment, the contents oflysine, citric acid, and water may be adjusted such that lysine andcitric acid are not precipitated into crystals or are formed intoprecipitates. When the adhesive composition is maintained in a liquidphase without forming crystals or precipitates, the adhesive compositionmay have excellent adhesion and may be uniformly applied to thesubstrate.

A mixing molar ratio of lysine to citric acid may be from 1.7:1 to 1:3.Particularly, the mixing molar ratio of lysine to citric acid may befrom 1.7:1 to 1:2, 1.7:1 to 1:1.5, 1.5:1 to 1:1.5, or 1.5:1 to 1:1. Whenthe content of lysine to that of citric acid is more than or less thanthe ranges described above, precipitates are formed in the composition,thereby decreasing adhesion or deteriorating storage stability orpreservation stability.

A solid content of the adhesive composition may be equal to or less than70 parts by weight, for example, from 0.1 to 70 parts by weight, from 1to 70 parts by weight, or from 10 to 70 parts by weight, based on 100parts by weight of the composition. When the solid content is within theranges described above, the adhesive composition may be easily appliedto the substrate. When the solid content is greater than 70 parts byweight, the composition cannot be used as an adhesive composition due tothe formation of precipitates in the adhesive composition. Although thesolid content decreases, the adhesive composition does not precipitateor lose the adhesive force. Thus, the solid content may be adjusted from0.1 to 10 parts by weight in accordance with application fields.

Citric acid and lysine may be included in the adhesive composition asactive ingredients. A sum of the contents of citric acid and lysine maybe from 60 to 100 parts by weight, from 70 to 99 parts by weight, from80 to 98 parts by weight, or from 85 to 97 parts by weight based on 100parts by weight of the solid content of the adhesive composition.

According to another aspect, citric acid and lysine may be included inthe form of a condensate including citric acid and lysine as a unit. Forexample, the condensate may be a dimer, a trimer, or an oligomer. Thecontent of the condensate may be equal to or less than 20 parts byweight, equal to or less than 10 parts by weight, or equal to or lessthan 1 part by weight, or 0 part by weight based on 100 parts by weightof the sum of the contents of the citric acid and lysine. When thecontent of the condensate is higher than the ranges described above, theadhesive force of the adhesive composition may decrease or the adhesivecomposition may not be maintained in the liquid phase.

The effects of the adhesive composition according to an embodiment onadhesion as described above will be described as follows. These andother effects are not to be construed as being limited to thosedescribed below and may also be explained by other effects within thescope of no scientific contradiction.

Lysine has two amino groups and citric acid has three carbonyl groups.An unshared electron pair of oxygen of a carbonyl group of citric acidmay interact with hydrogen of an amino group of lysine via an ionichydrogen bond.

Thus, when components of the adhesive composition according to anembodiment are analyzed by liquid chromatography of the like, lysine andcitric acid may be identified as raw materials. Thus, it may beconfirmed that lysine and citric acid are bonded via an ionic hydrogenbond in the adhesive composition and are present in the form of anaqueous solution of a salt. In the adhesive composition according to anembodiment, lysine and citric acid may have excellent adhesiveproperties while being maintained in a liquid phase at room temperature(25° C.) without forming crystals (solid state) or precipitates.

The adhesive composition according to the present disclosure has waterremovability. Thus, when the adhesive composition according to theembodiment is used as an adhesive, the adhesive is dissociated from thesubstrate or adherend to which the adhesive is applied by water, andthereby easily separated and removed therefrom. Particularly, theadhesive applied to the substrate or adherend may be dissociated within12 hours, particularly, within 6 hours, or more particularly, within 2hours at room temperature (25° C.) by a stirring or washing processusing water. The adhesive composition according to an embodiment iseasily dissociated by water and dissociated components are alsoenvironmentally friendly since they are not harmful to living organismsand the environment.

The adhesive composition according to the present disclosure may furtherinclude at least one alcohol solvent selected from a primary alcohol, apolyhydric alcohol, a dial, and a triol. When a solvent is further addedto the adhesive composition, a drying rate of the adhesive compositionmay be increased and processibilty of the adhesive composition may beimproved.

A mixing weight ratio of deionized water to alcohol in the adhesivecomposition according to the embodiment may be from 1:1 to 10:0. Moreparticularly, the mixing weight ratio of deionized water to alcohol inthe adhesive composition may be from 1:1 to 10:1, from 1:1 to 5:1, orfrom 1:1 to 3:2. As the content of alcohol increases in the adhesivecomposition, the adhesive composition is more efficiently dried and hasbetter coating, thereby increasing peel strength. However, when thecontent of alcohol is greater than 1.5 times or greater than that ofdeionized water in the adhesive composition, phase separation may occurin the adhesive composition.

The alcohol solvent may be a monohydric alcohol, a polyhydric alcohol,an unsaturated aliphatic alcohol, an alicyclic alcohol, or any mixturethereof. The monohydric alcohol may include at least one selected frommethanol, ethanol, propane-2-ol, butane-1-ol, pentane-1ol, andhexadecane-1-ol. The polyhydric alcohol may include at least oneselected from ethane-1,2-diol, propane-1,2-diol, propane-1,2,3-triol,butane-1,3-diol, butane-1,2,3,4-tetraol, pentane-1,2,3,4,5-pentol,hexane-1,2,3,4,5,6-hexol, and heptane-1,2,3,4,5,6,7-heptol.

The unsaturated aliphatic alcohol may include, for example, at least oneselected from prop-2-ene-1-ol, 3,7-dimethylocta-2,6-dien-1-ol,prop-2-yn-1-ol, cyclohexane-1,2,3,4,5,6-hexol, and2-(2-propyl)-5-methyl-cyclohexane-1-ol.

The pH of the adhesive composition may be from 2 to 11, particularly,from 2 to 9.5, more particularly, from 2 to 8.5. An adhesive compositionhaving the pH within the ranges described above has excellent storagestability and preservation stability and may not change in formulationor quality even after a long term storage. The adhesive composition mayhave excellent adhesion without forming precipitates when used not onlyimmediately after production but also after a long term storage.

Particularly, the adhesive composition may be a composition in whichprecipitates are not formed after being stored or distributed for 14days or more. For example, since the adhesive composition is stable,physical properties thereof may be maintained after being stored for 14days or more, for example, 12 months or more, for example, for 24 monthsor more. Also, a temperature of an environment in which the adhesivecomposition is stored may be from −18° C. to 80° C., particularly, −18°C. to 45° C., 0° C. to 60° C., or 20° C. to 40° C. Although the adhesivecomposition is stored in a temperature out of the temperature rangesabove, formulation and quality of the adhesive composition may not beaffected so long as a temperature of an environment in which theadhesive composition is used is within the ranges above. For example,when the adhesive composition is stored at a low temperature, theadhesive composition may be used after being maintained at roomtemperature for a predetermined time before use.

The adhesive composition according to the embodiment may have a contactangle of 15° to 70° when applied to the surface of the substrate.

The substrate may be any adherend commonly used in the art to which theadhesive composition is applicable. The substrate may be, for example, aglass substrate, a stainless steel (SUS) substrate, or a polymer film.As the polymer film, for example, a polyolefin film such aspolyethylene, polypropylene, an ethylene/propylene copolymer,polybutene-1, an ethylene/vinyl acetate copolymer, apolyethylene/styrenebutadiene rubber mixture, or a polyvinylchloridefilm may be generally used. In addition, a plastic material such aspolyethyleneterephthalate, polycarbonate, and poly(methylmethacrylate)or a thermoplastic elastomer such as polyurethane, and apolyamide-polyol copolymer, and any mixture thereof may also be used.When a glass substrate is used as the substrate, the adhesivecomposition may be more uniformly coated on glass having hydrophilicity,and thus a film forming property of the adhesive composition may beimproved. When an SUS substrate used as the substrate, citric acidincluded in the adhesive composition induces interactions with the SUS,and thus adhesion between the substrate and an adhesive layer formedfrom the adhesive composition is improved. When glass or SUS is used asthe substrate as described above, a contact angle of the adhesivecomposition with the substrate may decrease in comparison with apolyethylene film having hydrophobicity, and thus the adhesivecomposition may be more easily coated on the substrate.

As the solid content increases in the adhesive composition applied tothe substrate described above, the contact angle of the adhesivecomposition with the substrate decreases. When the contact angle of theadhesive composition with the substrate decreases as described above, anadhesive layer may be uniformly formed by applying the adhesivecomposition to the substrate and drying the composition and may haveimproved adhesive force to the substrate. The contact angle may bemeasured by using a contact angle meter via a Sessile Drop method. Thecontact angle may be measured by using, for example, a product ofPhoenix company (e.g.: Phoenix-150, Phoenix-MT, Phoenix-Alpha,Phoenix-Smart, Phoenix 300 Touch, or Phoenix-multi) with a drop volumeof 5 μl.

A contact angle of an adhesive layer formed of the adhesive compositionaccording to the present embodiment with the substrate may be from 15°to 70°. Specifically, a contact angle of the adhesive layer may decreasewith a substrate having a higher surface energy. According to anotherembodiment, the contact angle of the adhesive layer with a glasssubstrate may be, for example, equal to or less than 20°, for example,from 15° to 20°. A contact angle of the adhesive layer with a SUSsubstrate and the adhesive layer may be, for example, from 40° to 70°,and a contact angle of the adhesive layer with a polyethylene film maybe, for example, from 60° to 70°. According to another aspect of thepresent disclosure, a method of preparing the adhesive compositionincluding mixing lysine, citric acid, and water and stirring the mixtureat a temperature of 80° C. or less is provided.

When the mixing of lysine, citric acid, and water and stirring themixture is performed at a temperature out of the above-describedtemperature range, side reaction products, impurities, and the like maybe produced. In some cases, it may be difficult to obtain an adhesivecomposition having desired adhesion.

The stirring of the mixture at a temperature of 80° C. or less may beperformed at a temperature of, for example, 0° C. to 80° C. Moreparticularly, this step may be performed at a temperature of 0° C. to75° C., 0° C. to 70° C., 0° C. to 65° C., or 0° C. to 60° C.

The stirring of the mixture at a temperature of 80° C. or less mayinclude i) a first step of mixing and stirring at a temperature of, forexample, 0° C. to 80° C., 0° C. to 75° C., 0° C. to 70° C., or 0° C. to60° C. and ii) a second step of cooling to room temperature (20° C. to30° C.).

The mixing of lysine, citric acid, and water may be performed by addingcitric acid to an aqueous solution of lysine or by simultaneously mixinglysine, citric acid, and water.

The method may further include removing water and a solvent byconcentration under reduced pressure to control the solid content of theadhesive composition to a predetermined range.

According to another aspect of the present disclosure, an adhesiveproduct including the adhesive composition applied to the substrate isprovided. The adhesive product may include a substrate and an adhesivelayer obtained by applying the adhesive composition to the substrate anddrying the adhesive composition. The solvent included in the compositionmay be removed by drying. The drying may be performed at a temperatureof 25° C. to 45° C.

According to another aspect of the present disclosure, provided is amethod of attaching a first substrate to a second substrate including:applying the adhesive composition to the first substrate to bond theadhesive composition to the first substrate; and brining the firstsubstrate to which the adhesive composition is bonded into contact withthe second substrate to attach the first substrate to the secondsubstrate.

The first substrate and the second substrate may be each independentlyselected from glass, stainless steel, polymer film, metal, plastic,paper, fiber, and soil, without being limited thereto. For example, thefirst substrate may be formed of the same material as the secondsubstrate.

The adhesive composition or the adhesive product according to anembodiment, as a water-removable adhesive, may be used as adhesivetapes, spray-type adhesives for labeling, dust removers, or the like andmay be easily removed from an adherend by using water without damagingthe adherend, and packing materials may be easily recycled. In addition,when the adhesive composition or adhesive product is applied topesticides and seeds, an application range thereof may be widened due towater-removable properties thereof. The water-removable adhesiveaccording to the present embodiment may be manufactured with lowercosts, may be more easily handled, and may improve workability andcleanness of working environments in comparison with conventionalorganic solvent-type adhesives.

A bio-derived monomer may be selected as a starting material to preparethe adhesive composition according to the present embodiment. Since thebio-derived monomer may be used in living organisms, environmentalpollutions caused by petroleum-derived monomers, polymers, or oligomersobtained by separating the adhesive using water may be prevented inadvance. Structures such as adhesive tapes and sheets for labelsproduced by using the adhesive composition according to the presentembodiment as a water-removable adhesive have improved mechanicalstrength such as tensile strength and peel strength.

According to another embodiment, the adhesive composition or adhesiveproduct may further include at least one additive selected from areactive diluent, an emulsifier, a tackifier, a plasticizer, a filler,an antiaging agent, a curing accelerator, a flame retardant, acoagulant, a surfactant, a thickener, an UV screening agent, anelastomer, a pigment, a dye, a flavoring agent, an antistatic agent, anantiblocking agent, a slip agent, an inorganic filler, a kneading agent,a stabilizer, a modifying resin, a coupling agent, a levelling agent, afluorescent whitening agent, a dispersant, a thermal stabilizer aphotostabilizer, an UV absorbent, a wax, a wetting agent, anantioxidant, a preservative, and a lubricant. Although a total amount ofthe additives is not particularly limited, and various additives may beincluded in various weight ranges according to field of application. Theadditives may be used in amounts commonly used in the art, respectively.

The reactive diluent is a diluent assisting each component of thecomposition to be uniformly applied to an article to which thecomposition is applied and including at least one selected from, forexample, n-butylglycidylether, aliphaticglycidylether,2-ethylhexylglycidylether, phenylglycidylether, o-cresylglycidylether,nonylphenylglycidylether, p-tertbutylphenylglycidylether,1,4-butanedioldiglycidylether, 1,6-hexanedioldiglycidylether,neopentylglycidylether, 1,4-cyclohexanedimethyloldiglycidylether,polypropyleneglycoldiglycidylether, ethyleneglycoldiglycidylether,polyethyleneglycoldiglycidylether, diethyleneglycoldiglycidylether,resorcinoldiglycidylether, hydrogenated bisphenol-A glycidylether,trimethylolpropenetriglycidylether, glycerolpolyglycidylether,diglycerolpolyglycidylether, pentaerythritolpolyglycidylether, castoroil glycidylether, sorbitolpolyglycidylether, neodecanoic acidglycidylether, diglycidyl-1,2-cyclohexanedicarboxylate,diglycidyl-o-phthalate,N,N-diglycidylamine, N,N-diglycidyl-o-toluidine,triglycidyl-p-aminophenol, tetraglycidyl-diaminodiphenylmethane,triglycidyl-isocyanate, 1,4-butanedioldiglycidylether,1,6-hexanedioldiglycidylether, polypropyleneglycidyldiglycidylether, andtriethylolpropenetriglycidylether.

For example, the emulsifier may include at least one selected from acopolymer of polyoxyethylene and polyoxypropylene, a copolymer ofpolyoxyethylene and polyoctylphenylether, andsodiumdodecylbenzenesulfide.

Examples of the tackifier may be rosin and modified products thereof(e.g.: rosin, hydrogenated rosin, polymerized rosin, maleated rosin,rosin glycerin, and rosin modified phenolic resin), a terpene-basedresin (e.g.: a terpene resin, a terpene-phenol resin, a terpene-styreneresin, and a terpene-phenolic resin), a petroleum resin (e.g.: a C5petroleum resin, a C9 resin, a bicyclic nonadiene petroleum resin, ahydrogenated petroleum resin, and a styrene-terpene resin), a phenolicresin, a polymethylstyrene resin, a ketonealdehyde resin, a xyleneformaldehyde resin, a Cashew oil modified phenolic resin, a Tall oilmodified phenolic resin, rubber, a resin emulsion (e.g.: a rosinemulsion, a TPR water based resin, a 2402 resin emulsion, and apetroleum resin emulsion), a coumarone indene resin, and the like.

The plasticizer may improve processing flow or elongation. Theplasticizer may also improve functions of the composition, such aselectric insulation, adhesion, cold resistance, light resistance, oilresistance, resistance to saponification, flame retardancy, thermalstability, easy processibilty (intramolecular activity), activity(intermolecular activity), and non-toxicity.

A plasticizer to improve cold resistance may include dioctyl adiphate(DOA), dioctyl azelate (DOZ), dioctyl sebacate (DOS), Flexol TOF (UCCcompany), polyethyleneglycolester, and the like. A plasticizer toimprove heat resistance (non-volatility) and non-transmutation mayinclude a polymer blend such as polyester and nitrile-butadiene rubber(NBR), trimellitic ester, and pentarythritol ester. A plasticizer toimprove light resistance may include DOP, DOA, DOS, polyester, andepoxidized soybean oil (ESBO).

A plasticizer to improve oil resistance may include Phosflex aromaticphosphate ester (Product Name: TPP, TCP, 112 (CDP), and 179A (TXP)),polyester, NBR, and the like. A plasticizer to improve resistance tosaponification may include TCP, ESBO, polyester, and the like.

A plasticizer to improve flame retardancy may include phosphate such asTCP and TXP, chlorinated paraffin, chlorinated alkylstearate, NBR, andthe like. A plasticizer to improve thermal stability may include ESBO,DOZ, DOS, DOP, polyethyleneglycol ester, and the like.

A plasticizer to improve easy processibilty may include DOA, BBP, TOF,TCP, octyldiphenyl phosphate, and the like. A plasticizer to improveactivity may include DOZ, DOS, dibasic lead phosphate (DLP), ESBO,polyethyleneglycolester, and the like.

A plasticizer for non-toxicity may include BPBG, octyldiphenylphosphate,ESBO, ester of citric acid, NBR, and the like.

More particularly, examples of the plasticizer may includedibutylphthalate (DBP), dihexylphthalate (DHP), di-2-ethylhexylphthalate(DOP), di-n-octylphthalate (DnOP), diisooctylphthalate (DIOP),didecylphthalate (DDP), diisodecylphthalate (DIDP), C8-C10 mixed higheralcohol phthalate, butylbenzyl phthalate (BBP), dioctyladipate (DOA),dioctylazelate (DOZ), dioctylsebacate (DOS), tricresyl phosphate (TCP),trixylenyl phosphate (TXP), monooctyldiphenylphosphate (Santicizer141),monobutyl-dixylenyl phosphate, trioctylphosphate (TOF), aromatic oil,polybutene, paraffin, and the like.

As used herein, the thickener may be, for example, alginin, alginicacid, sodium alginate, guar gum, xanthan gum, collagen, alginate,gelatin, Furcellaran, agar, carrageenan, casein, locust bean gum,pectin, polyethyleneoxide, polyethyleneglycol, polyvinylalcohol, andpolyvinylpyrrolidone.

The surfactant may be any surfactant commonly used in the art. Forexample, the surfactant may include C8-C18 alkyl sulfate, alkyl ethersulfate or alkyl aryl ether sulfate having 8 to 18 carbon atoms, 40 orless of ethylene oxide or propylene oxide units, and a hydrophobicgroup, C8-C18 alkyl sulfonate, alkylaryl sulfonate, ester and semi-esterof sulfosuccinic acid including monohydric alcohol or alkylphenol, andalkyl polyglycol ether or alkyl aryl polyglycol ether having C8-C40ethylene oxide units. For example, sodium dodecyl sulfate (SDS),sodium-silicate, and the like may be used therefor.

The filler is added to improve strength, durability, and workability ofthe composition. Examples of the filler may include calcium carbonate,talc, ceramic, silica, dolomite, clay, titanium white, flowers of zinc,carbon (preventing shrinkage or blocking), potassium carbonate, titaniumoxide, liquid polysulfide polymer, volatile diluent, magnesium oxide,processing oil, and the like.

The curing accelerator may be, for example, dibutyltin dilaurate, JCS-50(Johoku Chemical Company Ltd.), or Formate TK-1 (Mitsui ChemicalPolyurethane Corporation). Te antiaging agent may be, for example,dibutyl hydroxy toluene (BHT), IRGANOX® 1010, IRGANOX® 1035FF, orIRGANOX® 565 (all manufactured by Chiba Specialty Chemicals).

The antistatic agent is not particularly limited and examples thereofmay include 1-hexyl-4-methylpyridinium hexafluorophosphate,dodecylpyridinium hexafluorophosphate, a fluorinated organometalliccompound (e.g., HQ-115 of 3M), an alkali metal salt (e.g., NaPF₆,NaSbF₆, KPF₆, and KSbF₆), a conductive polymer (e.g., polythiophene(PEDOT of Bayer), polyaniline, and polypyrrole), a metal oxide (e.g.,indium-doped tin oxide (ITO), antimony-doped tin oxide (ATO), tin oxide,zinc oxide, antimony oxide, and indium oxide), a quaternary ammoniumsalt (e.g., poly(acrylamide-co-diallyldimethyl ammonium chloride)solution of Sigma-Aldrich), 1-butyl-3-methylimidazoliumhexafluorophosphate [BMIM][PF₆], 1-butyl-3-(2-hydroxyethyl)imidazoliumbis(trifluoromethane sulfonyl)imide [BHEIM][NTf₂], andtetrabutylmethylammonium bis(trifluoromethanesulfonyl)imide [TBMA][NTf₂]which may be used alone or in combination of at least two thereof.

The elastomer refers to a rubber or a polymer having properties of anelastomer and may be, for example, ethylene-vinylacetate copolymer,acrylic rubber, natural rubber, isoprene rubber, styrene butadienerubber, chloroprene rubber, butyl rubber, ethylene propylene rubber,styrene-ethylene-butylene-styrene copolymer, or acrylonitrile-butadienecopolymer.

The stabilizer stabilizes the adhesive force of the adhesive compositionor the like and examples thereof may include polyhydric alcohol,polyvalent amine, or the like. For example, at least one selected fromalkylene glycol, dialkylene glycol, benzenediol, benzenetriol,dialcoholamine, trialcoholamine, arabitol, mannitol, isomalt, glycerol,xylitol, sorbitol, maltitol, erythritol, ribitol, dulcitol, lactitol,threitol, iditol, polyglycitol, alkylene diamine, alkenylene diamine,phenylene diamine, and n-aminoalkylalkane diamine may be used therefor.

The fluorescent whitening agent may be a benzooxazole compound, abenzothiazole compound, a benzoimidazole compound, or the like.

The pigment may be a natural pigment or a synthetic pigment or aninorganic pigment or an organic pigment classified by another criterion.

The flavoring agent may be, for example, but is not limited to,peppermint oil, spearmint oil, carvone, or menthol, used alone or incombination.

The flame retardant may be melamine cyanurate, magnesium hydroxide,agalmatolite, zeolite, sodium silicate, aluminum hydroxide, antimony(antimony trioxide), or the like. An additive to improve waterresistance may be glyoxal.

Examples of the modifying resin may include a polyol resin, a phenolresin, an acrylic resin, a polyester resin, a polyolefin resin, an epoxyresin, and an epoxidized polybutadiene resin.

The coupling agent may improve adhesion and adhesion reliability betweenthe adhesive composition and a packaging material. If the coupling agentis added, adhesion reliability may be improved in the case where acomposition is maintained under high-temperature and/or high-humidityconditions for a long period of time. Examples of the coupling agent mayinclude a silane compound such as γ-glycidoxypropyl triethoxy silane,γ-glycidoxypropyl trimethoxy silane, γ-glycidoxypropyl methyldiethoxysilane, γ-glycidoxypropyl triethoxy silane, 3-mercaptopropyl trimethoxysilane, vinyltrimethoxysilane, vinyltriethoxy silane,γ-methacryloxypropyl trimethoxy silane, γ-methacryloxy propyl triethoxysilane, γ-aminopropyl trimethoxy silane, γ-aminopropyl triethoxy silane,3-isocyanato propyl triethoxy silane, γ-acetoacetatepropyltrimethoxysilane, γ-acetoacetatepropyl triethoxy silane, β-cyanoacetyltrimethoxy silane, β-cyanoacetyl triethoxy silane, and acetoxyacetotrimethoxy silane.

The kneading agent may be aromatic hydrocarbon resin.

The antiaging agent may be N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine.

The wetting agent may be, for example, sugar, glycerin, a sorbitolaqueous solution, or an amorphous sorbitol aqueous solution, used aloneor in combination.

The UV absorbent may be ethylhexyl methoxycinnamate (e.g., 2-ethylhexyl4-methoxycinnamate), ethylhexylsalicylate, 4-methylbenzylidene camphor,isoamyl p-methoxycinnamate, octocrylene, phenylbenzimidazole sulfonicacid, homosalate, cynoxate, ethylhexyltriazone, polysilicone-15,TEA-salicylate, PABA, ethylhexyldimethyl PABA, glyceryl PABA, or thelike. These compounds may be used alone or in combination of at leasttwo.

The adhesive composition or adhesive product according to the presentdisclosure may further include additives disclosed in U.S. Pat. No.4,959,412, CA1278132, U.S. Pat. No. 6,777,465, WO2007-120653,US2003-0064178, U.S. Pat. Nos. 7,306,844, 7,939,145, WO2011-136568,WO2010-071298, Korean Patent Application Publication No. 2016-0095132,Japanese Patent Application Publication No. 5959867, Korean Patent No.989942, which are hereby incorporated by reference, in addition to theabove-described additives.

The adhesive composition or adhesive product according to an embodimentmay be used to attach labels or the like to various packing materialsincluding metal, glass, and plastic. The packing materials may be, forexample, containers for food, beverage, or household products, and thesecontainers may be made of glass, metal, or plastic.

The adhesive composition or adhesive product may be used as adhesives,coating agents, carriers, food additives, or the like according to thecomposition and characteristics thereof.

When used as adhesives, the adhesive composition or adhesive productaccording to the present disclosure may be used as adhesives for labels,sealants, wallpaper, cigarette paper, adhesive block toys, sandsculpture, food, bath/kitchen detergents, animal ointment sprays,exfoliation, hair fixation, hair gel, soil stabilizers, waterdispersion, strength agents on paper, corrugated board, zone adhesives,and the like. The soil stabilizers are used to remove fine dusts such assandy dusts or dusts generated in factories.

When used as coating agents, the adhesive composition or adhesiveproduct according to the present disclosure may be used for forest fireprevention, fruits and vegetables, truncated surfaces of flowers, dyes,antifouling pretreatment coating agents, and the like. In this case, theantifouling pretreatment coating agents may be coated on an easilycontaminated medium and then contaminants may be simply removedtherefrom by washing with water.

When used as carriers, the adhesive composition or adhesive productaccording to the present disclosure may be applied to forest protectionagainst epidemics, forest fire prevention, air fresheners for bathrooms,disinfectants, agricultural materials, household products, toys, and thelike. The forest protection against epidemics may be, for example,prevention of the spread of diseases such as pinewood nematode inforests. The disinfectants include, for example, avian influenzadisinfectants and foot-and-mouth disease disinfectants. The agriculturalmaterials may include fertilizers, taping materials, and seed coatings.

When used as agricultural materials, the adhesive composition oradhesive product according to the present disclosure may be applied toseed-coating agents, plant taping agents, insecticide additives,fertilizer excipients, natural pesticides, and the like. When used ashousehold products, the adhesive composition according to the presentdisclosure may be added to paints to enhance adhesive forces thereof topaper without draining off or added to food colors to prepare ediblepaints used by toddlers. Another examples of household products, theadhesive composition may also be used as a decontamination pretreatmentagent. Mores particularly, contaminants may be quickly removed byspraying the adhesive composition according to the present disclosure tocontaminated media such as window screens, window frames, andautomobiles and then washing the media with water.

When used as carriers, the adhesive composition or adhesive productaccording to the present disclosure may realize oxygen-blocking,moisture-blocking, oil-resistant, and heat-sealing functions. Thus, whenused in coating layers of eco-friendly food packing materials, effectsof preventing or delaying decay and oxidation of food may be obtainedwhile inhibiting infiltration of external moisture. Also, when used asfood additives, the adhesive composition or adhesive product accordingto the present disclosure may be applied to wheat gluten substitutes,jellys, starch syrups, cookies, food colors, ice creams, and antifreezesubstances.

Hereinafter, one or more embodiments of the present disclosure will bedescribed in detail with reference to the following examples. Theseexamples are not intended to limit the purpose and scope of the one ormore example embodiments of the present disclosure.

Example 1: Evaluation of Stability of Composition Including Lysine andVarious Organic Acids

Lysine, as basic amino acid, and various organic acids were mixed toprepare compositions. Stability of each composition (whether or notprecipitates are formed) was evaluated.

Method of Preparing Adhesive Composition Including Lysine and CitricAcid:

79 g of distilled water (DIW) was added to 100 g of a 54 wt % aqueoussolution of L-lysine free form while stirring the mixture at roomtemperature (25° C.) for 30 minutes to dilute lysine. 70.97 g of citricacid (CA) was slowly added to the diluted lysine at room temperature(25° C.) for 1 hour while stirring and then the mixture was furtherstirred at 60° C. for 1 hour. Then, the reaction mixture was cooled toroom temperature (25° C.) to terminate the reaction and obtain 249.93 gof an adhesive composition. A solid content of this composition wasabout 50 parts by weight based on 100 parts by weight of thecomposition, a mixing molar ratio of lysine to citric acid was 1:1, anddeionized water was used as a solvent.

Compositions were prepared in the same manner as described above byusing different types of organic acids. The compositions were preparedin the same manner as in Example 1, except that organic acids shown inTable 1 below were used.

TABLE 1 Solid content Lysine:acid (parts by No. Acid (mol ratio) Solventweight) 1-1 Citric acid 1:1 DIW 50 1-2 Acetic acid 1:1 1-3 Glutamic acid1:1 1-4 Glutaric acid 1:1 1-5 Tartaric acid 1:1 1-6 Aspartic acid 1:11-7 Fumaric acid 1:1 1-8 Glyoxylic acid 1:1 1-9 4-ketopimelic acid 1:11-10 Pyruvic acid 1:1 1-11 1,3-acetonedicarboxylic acid 1:1

Formation of precipitates of the compositions prepared according toTable 1 was evaluated. Particularly, each of the compositions wasapplied to an OPP film (Sam Young Chemical Co., Ltd.) having a thicknessof 50 μm by using a bar coater to a thickness of about 50 μm. After thefilm coated with the composition was maintained at room temperature (25°C.) at a relative humidity of 60±10% for 14 days, changes on the surfaceof the adhesive composition present on the OPP film were identified andevaluated. Evaluation results are shown in Table 2 below.

TABLE 2 Solid content Lysine:acid (parts by No. Acid (mol ratio) Solventweight) State 1-1 Citric acid 1:1 DIW 50 Liquid state 1-2 Acetic acid1:1 Precipitates 1-3 Glutamic acid 1:1 Precipitates 1-4 Glutaric acid1:1 Precipitates 1-5 Tartaric acid 1:1 Precipitates 1-6 Aspartic acid1:1 Precipitates 1-7 Fumaric acid 1:1 Precipitates 1-8 Glyoxylic acid1:1 Precipitates 1-9 4-ketopimelic 1:1 Precipitates acid 1-10 Pyruvicacid 1:1 Precipitates 1-11 1,3-acetonedi- 1:1 Precipitates carboxylicacid

Referring to the results shown in Table 2, while precipitates were notformed in the composition including lysine and citric acid, precipitateswere formed in the compositions including the other organic acids andlysine making evaluation of adhesion impossible. That is, in the casewhere compositions are prepared by mixing lysine and various organicacids, it was confirmed that not all of the compositions haveadhesiveness without forming precipitates.

Example 2: Evaluation of Solubility According to Solvent of Composition

Adhesive compositions including lysine and citric acid were prepared inthe same manner as in Example 1. 25 g of an additional solvent shown inTable 3 below was added 50 g of each of the prepared adhesivecompositions (molar ratio of lysine to citric acid=1:1 and solidcontent: 50 parts by weight) and the mixture was stirred for 1 hour.After stirring, solubility of the adhesive composition to each solventwas identified. Types of the added solvent and evaluation results ofsolubility of the adhesive composition to each solvent are shown inTable 3 below.

TABLE 3 No. Added solvent Solubility 2-1 Methanol Dissolved 2-2 TolueneUndissolved 2-3 Benzene Undissolved 2-4 Chloroform Undissolved 2-5Methylenechloride Undissolved 2-6 Dichloromethane Undissolved 2-7Tetrahydrofuran (THF) Undissolved 2-8 Ethyl acetate Undissolved 2-9Dimethylformamide(DMF) Undissolved 2-10 Dimethylsulfoxide (DMSO)Undissolved 2-11 n-hexane Undissolved

Referring to Table 3, the adhesive composition according to the presentdisclosure was dissolved in an alcohol such as methanol used as asolvent, but not dissolved in the other organic solvents.

Example 3: Analysis of State, Viscosity, and Initial Tack of AdhesiveComposition According to Mixing Molar Ratio of Lysine to Citric Acid

Stability, viscosity, and initial tack of adhesive compositions of thepresent disclosure according to the molar ratio of lysine to citric acidincluded in the adhesive compositions were analyzed.

Adhesive compositions including lysine and citric acid were prepared inthe same manner as in Example 1 by adjusting molar ratios of lysine tocitric acid to 3:1. 2.5:1, 2:1, 1.5:1, 1:1, 1:1.5, 1:2, 1:2.5, and 1:3,respectively (solid content: 50 parts by weight).

(1) Evaluation of Stability

Stability of the adhesive compositions having various molar ratios wasevaluated according to the following method. About 1 g of each of theadhesive compositions was applied to an aluminum dish having a diameterof 5 cm. Then, formation of precipitates was identified in the adhesivecomposition under the following drying conditions.

i) Drying Conditions 1

The adhesive compositions were maintained at room temperature (25° C.)at a relative humidity of 60±10% for 14 days to identify formation ofprecipitates and changes on the surfaces thereof.

ii) Drying Conditions 2

The adhesive composition were maintained in an oven at 40° C. for 48hours to identify formation of precipitates and changes on the surfacesthereof.

(2) Evaluation of Viscosity

Viscosity was measured using a rotary viscometer (Manufacturer:LAMYRHEOLOGY, Product Name: RM200 TOUCH CP400 or RM200 TOUCH) at 25±1°C. using a LV-1 spindle at 60 rpm.

(3) Evaluation of Initial Tack

Initial tacks of the adhesive compositions in which precipitates werenot formed in the evaluation of stability were evaluated. Initial tacksof the adhesive compositions were measured by a rheometer of Anton Paar,Co., Ltd and compared using the rheometer. A SUS probe having a diameterof 25 mm was brought into contact with each adhesive composition for 1minute to maintain a gap of 0.01 mm, and then a force generated toseparate the probe at the same speed was measured to quantitativelyevaluate an instantaneous initial tack.

Evaluation results are shown in Table 4 below.

TABLE 4 Solid content Initial Lysine:CA (parts by Viscosity tack No.(mol ratio) weight) (mPa · s) (mJ) State Note 3-1 3:1 50 40.77 —Precipitates Room temperature: A of FIG. 3 Oven: A of FIG. 4 3-2 2.5:1  36.54 — Precipitates Room temperature: B of FIG. 3 Oven: B of FIG. 4 3-32:1 32.53 — Precipitates Room temperature: C of FIG. 3 Oven: C of FIG. 43-4 1.5:1   28.84 0.245 Liquid state Room temperature: D of FIG. 3 Oven:D of FIG. 4 3-5 1:1 26.68 0.222 Liquid state 3-6   1:1.5 25.76 0.22Liquid state 3-7 1:2 23.31 0.215 Liquid state 3-8   1:2.5 22.15 0.213Liquid state 3-9 1:3 20.12 0.212 Liquid state

*In Table 4, room temperature refers to drying conditions 1 and ovenrefers to drying conditions 2.

Referring to Table 4, precipitates were formed in the adhesivecompositions in which the molar ratio of lysine to citric acid was inthe range of 3:1 to 2:1.

While precipitates were formed in the adhesive composition in which themolar ratio of lysine to citric acid was 2:1, precipitates were notformed at a molar ratio of lysine to citric acid of 1.5:1. In order toidentify a more specific critical point, adhesive compositions wereprepared by subdividing the molar ratio of lysine to citric acid into2:1, 1.9:1, 1.8:1, 1.7:1, 1.6:1, and 1.5:1 (where the solid content was50 parts by weight). Then, stability, viscosity, and initial tackthereof were evaluated in the same manner.

Evaluation results are shown in Table 5 below.

TABLE 5 Solid Initial Lysine:CA content Viscosity tack No. (mol ratio)(wt %) (mPa · s) (mJ) State 3-10  2:1 50 32.53 — Precipitates 3-11 1.9:131.76 — Precipitates 3-12 1.8:1 30.11 — Precipitates 3-13 1.7:1 29.450.255 Liquid state 3-14 1.6:1 28.90 0.249 Liquid state 3-15 1.5:1 28.840.245 Liquid state

Referring to Table 5, while precipitates were formed at a molar ratio oflysine to citric acid of 2:1 to 1.8:1, precipitates were not formed at amolar ratio of lysine to citric acid of 1.7:1 to 1.5:1.

Example 4: Analysis of State, Viscosity, and Initial Tack of AdhesiveComposition According to Solid Content

State, viscosity, and initial tack of the adhesive compositions of thepresent disclosure according to the solid content were analyzed.

1) Evaluation According to Solid Content at a Molar Ratio of Lysine toCitric Acid of 1:1

Adhesive compositions including lysine and citric acid were prepared inthe same manner as in Example 1, except that solid contents in theadhesive compositions were adjusted to 10 wt %, 20 wt %, 30 wt %, 40 wt%, 50 wt %, 60 wt %, 70 wt %, and 75 wt % respectively (where the molarratio of lysine to citric acid was 1:1). Here, the solid content wasadjusted by using water.

States, viscosity, and initial tack of the compositions were evaluatedin the same manner as in Example 3. Evaluation results are shown inTable 6 below.

TABLE 6 Solid Initial Lysine:CA content Viscosity tack No. (mol ratio)(wt %) (mPa · s) (mJ) State 4-1 1:1 10 10.08 0.21 Liquid state 4-2 1:120 11.84 0.217 Liquid state 4-3 1:1 30 13.54 0.216 Liquid state 4-4 1:140 16.24 0.22 Liquid state 4-5 1:1 50 26.68 0.222 Liquid state 4-6 1:160 85.28 0.523 Liquid state 4-7 1:1 70 657.67 1.48 Liquid state 4-8 1:175 Insoluble material (CA)

Referring to Table 6, it was confirmed that the solid content are notdissolved in the adhesive composition and precipitates were formed whenthe solid content in the compositions was 75 wt %.

While precipitates were formed when the solid content in thecompositions was 75 wt %, precipitates were not formed when the solidcontents in the compositions were 60 wt % and 70 wt %. In order toidentify a more specific critical point, adhesive compositions wereprepared by subdividing the solid content into 60 wt %, 61 wt %, 62 wt%, 63 wt %, 64 wt %, 65 wt %, 66 wt %, 67 wt %, 68 wt %, 69 wt %, 70 wt%, 71 wt %, and 72 wt % in the compositions (where the molar ratio oflysine to citric acid was 1:1). Then, stability, viscosity, and initialtack thereof were evaluated in the same manner.

Evaluation results are shown in Table 7 below.

TABLE 7 Solid Initial Lysine:CA content Viscosity tack No. (mol ratio)(wt %) (mPa · s) (mJ) State 4-9 1:1 60 85.28 0.523 Liquid state 4-10 1:161 91.45 0.562 Liquid state 4-11 1:1 62 99.13 0.614 Liquid state 4-121:1 63 115.22 0.652 Liquid state 4-13 1:1 64 125.35 0.751 Liquid state4-14 1:1 65 168.5 0.783 Liquid state 4-15 1:1 66 184.15 0.899 Liquidstate 4-16 1:1 67 233.56 0.921 Liquid state 4-17 1:1 68 290.52 1.12Liquid state 4-18 1:1 69 424.2 1.24 Liquid state 4-19 1:1 70 657.67 1.48Liquid state 4-20 1:1 71 Insoluble material (CA) 4-21 1:1 72 Insolublematerial (CA)

Referring to Table 7, while the adhesive compositions were maintained inliquid states when the solid content was 70 wt % in the adhesivecomposition, precipitates were formed within two weeks when the solidcontent was 71 wt % or greater in the adhesive composition.

2) Evaluation According to Solid Content at a Molar Ratio of Lysine toCitric Acid of 1:2, 1:3, or 2:1

Formation of precipitates according to the solid content was evaluatedwhile the molar ratio of lysine to citric acid varies.

Adhesive compositions including lysine and citric acid were prepared inthe same manner as in Example 1, except that the molar ratios of lysineto citric acid were adjusted to 1:2, 1:3, and 2:1, respectively. Thecontent of water was adjusted such that the solid contents of thecompositions were adjusted to 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt%, 60 wt %, 70 wt % respectively. Stability of the compositions wereevaluated in the same manner as in Example 1. Evaluation results areshown in Table 8 below.

TABLE 8 Solid Lysine:CA content No. (mol ratio) (wt %) State 4-22 1:2 10Liquid state 4-23 20 Liquid state 4-24 30 Liquid state 4-25 40 Liquidstate 4-26 50 Liquid state 4-27 60 Liquid state 4-28 70 Liquid state4-29 1:3 10 Liquid state 4-30 20 Liquid state 4-31 30 Liquid state 4-3240 Liquid state 4-33 50 Liquid state 4-34 60 Liquid state 4-35 70 Liquidstate 4-36 2:1 10 Precipitates 4-37 20 Precipitates 4-38 30 Precipitates4-39 40 Precipitates 4-40 50 Precipitates

Referring to Table 8, precipitates were not formed at molar ratios oflysine to citric acid of 1:2 and 1:3 although the solid contents varyfrom 10 wt % to 70 wt %. However, precipitates were formed when themolar ratio of lysine to citric acid was 2:1 regardless of the soldcontent.

That is, it may be confirmed that the molar ratio of lysine to citricacid is the most important factor affecting stability and adhesive forceof the adhesive composition according to the present disclosure. At thesame molar ratio of the lysine to citric acid, stability and adhesiveforce of the adhesive composition is affected by the solid content.

Example 5: Comparison of Initial Tack and Water Removability

Adhesive forces and water removability were compared between aconventional adhesive and the adhesive composition according to thepresent disclosure.

Adhesive compositions including lysine and citric acid were prepared inthe same manner as in Example 1, except that the solid content wasadjusted to 10 wt % in the adhesive compositions by adjusting thecontent of water (where the molar ratio of lysine to citric acid was1:1)

A commercially available polyvinyl alcohol-based adhesive (PVA 088-50,Qingdao Sanhuan Colorchem CO., LTD.) was prepared and the solid contentwas adjusted to 10 wt % by controlling the content of water(hereinafter, referred to as Control 1).

Viscosity and initial tack of the adhesive compositions according to thepresent disclosure (solid content: 10 wt %) and Control 1 were evaluatedin the same manner as in Example 3.

Water removability of the adhesive compositions according to the presentdisclosure (solid content 10 wt %) and Control 1 was evaluated. Waterremovability was evaluated according to the following method. Theadhesive composition according to the present disclosure was applied toa PET film to a thickness of 50 to 60 μm and dried at 40° C. for 30minutes. A dried resultant was cut to a size of 25 mm×25 mm and attachedto a stainless steel (SUS304) by pressing five times at a pressure of 2kgf by using a hand roller to prepare a sample. A PVA adhesive wasapplied to a PET film to a thickness of 50 to 60 μm, cut to a size of 25mm×25 mm, attached to a stainless steel (SUS304) by pressing five timesat a pressure of 2 kgf by using a hand roller to prepare a sample.

Each of the samples was completely immersed in distilled water (DIW) atroom temperature, atmospheric pressure, and a neutral pH and stirred at200 rpm by using a stirrer. States of the samples were identified i)after 1 hour or ii) after 24 hours. Then, periods of time during whichthe samples according to the present disclosure and the adhesive ofControl 1 were completely removed were measured to evaluate waterremovability of the samples.

Evaluation results are shown in Table 9 below.

TABLE 9 Solid Initial content Viscosity tack (wt %) (mPa · s) (mJ) Waterremovability 5-1 10 10.1 0.21 Separated within 1 hour Control 1 10 43.490.201 i) partially dissolved (PVA-based) in water after 1 hour or ii)dissolved in water after 24 hours, at 200 rpm.

Referring to Table 9, the adhesive composition according to the presentdisclosure exhibited a similar initial tack and was quickly separated inwater in comparison with the PVA-based adhesive composition (Control 1).On the contrary, the PVA-based adhesive composition was dissolved inwater after 24 hours but partially dissolved in water after 1 hour.

That is, the adhesive composition according to the present disclosurehas a similar or better adhesive force and far better water removabilitythan conventional adhesives, and thus it is expected to utilize theadhesive composition according to the present disclosure in variousfields.

Example 6: Evaluation of Peel Strength and Water Removability Accordingto Solvent

Adhesive compositions including lysine and citric acid were prepared inthe same manner as in Example 1 (6-1 to 6-3 below), except that themolar ratios of lysine to citric acid were adjusted to 1.5:1, 1:1, and1:1.5 (where the solid content was 50 parts by weight)

Adhesive compositions including lysine and citric acid were furtherprepared in the same manner as in Example 1 (6-4 to 6-6 below), exceptthat molar ratios of lysine to citric acid were adjusted to 1.5:1, 1:1,and 1:1.5, and methanol was further added thereto as a solvent. Here, aweight ratio of deionized water to methanol was 1:1 (where the solidcontent was 50 parts by weight).

Additionally, adhesive compositions including lysine and citric acidwere prepared in the same manner as in Example 1 (6-7 to 6-8 below),except that methanol was further added thereto in addition to deionizedwater and weight ratios of deionized water to methanol were 6:4 and 4:6.(where the molar ratio of lysine to citric acid was 1:1, and the solidcontent was 50 parts by weight).

As a control, a commercially available acrylic adhesive (K901, HansungP&I, hereinafter, referred to as Control 2, where the solid content was59 wt %) was prepared. Peel strength and water removability of theadhesive compositions were evaluated according to the following methods,and evaluation results are shown in Table 10 below.

1) Peel Strength

PET films were prepared (film standards: 120 mm×25 mm and thicknesses:38 μm or 50 μm), and a sample was coated to a surface of the PET film(having a thickness of 50 μm) to a thickness of 11 μm by using a barcoater. Then, the PET film was dried in an oven at 60° C. for 4 minutesand then laminated on a PET film (having a thickness of 38 μm) by usinga dry laminator (at a roller speed of 1.9 m/min and a roller temp. of60° C.). The laminated sample was dried in an oven at 30° C. for 72hours. Peel strength of the dried sample was measured in accordance withthe ASTM D1876 “180° T peel strength measurement” method.

2) Water Removability

The prepared adhesive compositions according to the present disclosureand Control 2 were applied to the PET film to a thickness of 50 to 60 μmand dried at 40° C. for 30 minutes.

Dried resultants were cut to a size of 25 mm×25 mm and attached to astainless steel (SUS304) by pressing five times at a pressure of 2 kgfby using a hand roller to prepare samples.

Each of the samples was completely immersed in distilled water (DIW) atroom temperature, atmospheric pressure, and a neutral pH and stirred at200 rpm by using a stirrer. States of the samples were identified i)after 1 hour or ii) after 24 hours

TABLE 10 Solid Peel content strength Lysine:CA (parts by (N/25 Water No.(mol ratio) Solvent weight) mm) removability 6-1 1.5:1  DIW 50 5.91Completely 6-2 1:1 5.45 dissolved in 6-3  1:1.5 4.92 water 6-4 1.5:1 DIW and 7.11 i) after 1 6-5 1:1 methanol 6.92 hour or 6-6  1:1.5 (1:1 in6.18 ii) after 24 weight) 6-7 1:1 DIW and 6.28 hours, methanol at 200rpm. (6:4 in weight) 6-8 1:1 DIW and — Phase methanol separation (4:6 inweight) Control 2 — 59 6.61 Undissolved (acrylic) in water

Referring to Table 10, an adhesive product obtained by using theadhesive composition according to the present disclosure was separatedwithin 1 hour after being immersed in water. In addition, it wasconfirmed that peel strength was further increased when the alcoholsolvent is further used together with water. These results may beobtained because the adhesive composition including a mixed solvent hasa lower contact angle than that including only deionized water andbetter coating properties on a substrate film. However, when a weightratio of deionized water to alcohol was 4:6, phase separation occurredin the adhesive composition. Although the adhesive composition accordingto the present disclosure exhibited similar peel strength even with alower solid content in comparison with the conventional acrylic adhesive(Control 2). However, the acrylic adhesive was not dissolved in watereven after 25 hours.

Example 7: Composition Analysis of Adhesive Composition According toReaction Temperature

Composition of adhesive compositions according to reaction temperaturewere analyzed.

1) Preparation at 0° C. (low temperature): 79 g of DIW was added to 100g of a 54 wt % aqueous solution of lysine and the mixture was stirred at0° C. (T1) for 30 minutes. The diluted resultant was stirred whileadding 70.97 g of citric acid thereto at 0° C. (T2) for 1.5 hours toprepare an adhesive composition (solid content: 50 wt % and mixing ratioof lysine to citric acid=1:1). An ice bath was used to maintain the sametemperature of the adhesive composition while stirring.

2) Preparation at 25° C. (room temperature): 79 g of DIW was added to100 g of a 54 wt % aqueous solution of lysine and the mixture wasstirred at room temperature (T1) for 30 minutes. The diluted resultantwas stirred while adding 70.97 g of citric acid thereto at 25° C. (T2)for 1.5 hours to prepare an adhesive composition (solid content: 50 wt %and mixing ratio of lysine to citric acid=1:1). A temperature controllerwas used to maintain the same temperature while stirring (The samemethod is used in the following cases).

3) Preparation at 60° C.: An adhesive composition was prepared in thesame manner as in the above method 2), except that T2 was changed to 60°C.

4) Preparation at 80° C.: An adhesive composition was prepared in thesame manner as in the above method 2), except that T2 was changed to 80°C.

5) Preparation at 240° C.: An adhesive composition was prepared in thesame manner as in the above method 2), except that T2 was changed to240° C.

As a result of preparing the compositions as described above, carbidewas formed at 240° C., making it impossible to produce an adhesivecomposition. Thus, composition analysis was performed on thecompositions prepared at 0° C., 25° C., 60° C., and 80° C. using ¹H NMR.

An NMR spectrometer and analysis conditions used in the presentdisclosure are as follows.

Superconducting Fourier transform nuclear magnetic resonancespectrometer (400 MHz) (Model No.: AVANCE II 400, Manufacturer: BrukerBiospin (Magnet field strength 9.4 Tesla, Field drift rate: 4 Hz/hr,Observable Frequency: 400 Mhz 1H, Sensitivity: 220:1(1H), VariableTemp.: −70 to +110° C.), and solvent: D₂O)

The compositions prepared at 0° C., 25° C., and 80° C. were analyzed byusing ¹H NMR. NMR analysis results are shown in FIG. 1. Referring toFIG. 1, ¹H NMR peaks were observed at the same position in thecompositions prepared at 0° C., 25° C., and 80° C., and no chemicalshift was observed. Thus, it was confirmed that the compositions had thesame composition. That is, lysine and citric acid are present in a mixedstate and no condensate, or very little condensate, of lysine and citricacid was generated in the adhesive compositions prepared at 0° C., 25°C., and 80° C.

Example 8: Composition Analysis of Adhesive Composition According toReaction Time

Composition ratios of adhesive compositions according to reaction timewere analyzed.

1) Preparation at 60° C.: 7.56 g of DIW was added to 100 g of a 54 wt %aqueous solution of lysine and the mixture was stirred at 25° C. (T1)for 30 minutes. The diluted resultant was stirred while slowly adding70.97 g of citric acid thereto at 60° C. (T2) for 9 hours to prepare anadhesive composition (solid content: 70 wt % and mixing ratio of lysineto citric acid=1:1). Composition analysis was performed on the adhesivecomposition at every 3 hours.

2) Preparation at 80° C.: An adhesive composition was prepared in thesame manner as in the above method 1), except that T2 was changed to 80°C. Composition analysis was performed on the adhesive composition atevery 3 hours.

Composition analysis was performed on the prepared compositions by HPLC.

Analysis results are shown in Table 1 below.

TABLE 11 Reaction Amount of Amount of time Lysine Citric acidTemperature (hr) (wt %) (wt %) 80° C. 0 38.34 29.83 3 37.33 28.93 636.29 28.17 9 35.22 26.97 60° C. 0 39.43 30.24 3 39.04 30.14 6 39.7130.28 9 39.15 30.01 12 38.49 29.94

Referring to Table 11, after addition of citric acid, the weights oflysine and citric acid were maintained at the almost same levels (withinexperimental error) in the adhesive composition prepared by stirring at60° C. However, after addition of citric acid, the amounts of lysine andcitric acid were slightly reduced in the adhesive composition preparedby stirring at 80° C. Thus, it may be estimated that a small amount of acondensate of lysine and citric acid was generated. As a result ofanalyzing the other substances except for lysine and citric acid, theamount of the condensate was less than 10 wt % based on a total ofinitial weights of lysine and citric acid.

Example 9: Evaluation of Contact Angle of Substrate with AdhesiveComposition

Contact angles of the adhesive compositions with substrates weremeasured by using a contact angle meter (Product name: phoenix,measurement conditions: drop volume 5 μl). Contact angles may bemeasured by dropping a predetermined amount of a liquid by using a micropipet or a syringe and measuring an angle of a droplet via software. Ingeneral, a lower contact angle may be evaluated as a better adhesive.

Adhesive compositions including lysine and citric acid were prepared inthe same manner as in Example 1, except that the solid contents wereadjusted to 10 wt %, 20 wt % and 30 wt % in the adhesive compositions,respectively (where the molar ratio of lysine to citric acid was 1:1).The solid content was adjusted by controlling the amount of water.

Contact angles of the adhesive compositions according to the presentdisclosure were evaluated using glass, SUS, and PE as substrates. In acontrol, diiodomethane and distilled water were used.

Contact angle measurement results are shown in FIG. 2.

Referring to FIG. 2, since a glass substrate is a hydrophilic substrate,diiodomethane that is a non-polar compound had a relatively high contactangle with the glass substrate and distilled water had a relatively lowcontact angle therewith. Since the adhesive composition having the solidcontent of 10 parts by weight is applied thereto, polarity decreases andthus a contact angle thereof with the substrate increases. However, thecontact angle of the adhesive composition decreased as the solid contentincreased in the adhesive composition that is a hydrophilic substance.

When an SUS substrate was used, citric acid included in the adhesivecomposition induces interactions with SUS. Thus, as the solid contentincreases in the adhesive composition, the contact angle decreases withthe SUS substrate. In addition, a PE substrate is hydrophobic. Thus,when the non-polar diiodomethane is applied to the PE substrate, acontact angle of diiodomethane with the PE substrate is relatively lowand a contact angle of distilled water is relatively high. Sincepolarity of distilled water decreases by adding the adhesivecomposition, the contact angle was slightly decreased. As a result, itwas confirmed that the contact angle of the adhesive composition with asubstrate decreases when the adhesive composition according to thepresent disclosure is applied to a hydrophilic substrate or a substratehaving a high surface energy.

As described above, the adhesive composition according to the presentdisclosure may be used as a water-removable adhesive, a coating agent,and a carrier. When used as the water-removable adhesive, the adhesivecomposition may be easily removed from an adherend or a substrate bywater. Thus, the adhesive is echo-friendly due to water removability.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the inventive concept as definedby the following claims.

What is claimed is:
 1. An adhesive composition comprising lysine, citricacid, and water, wherein the lysine and the citric acid are present inthe form of an aqueous solution of a salt and do not form precipitatesin the aqueous solution.
 2. The adhesive composition of claim 1, whereinthe precipitates are precipitates of the lysine and the citric acid. 3.The adhesive composition of claim 1, wherein a mixing molar ratio of thelysine to the citric acid is adjusted such that precipitates of thelysine and the citric acid are not formed in the adhesive composition.4. The adhesive composition of claim 3, wherein the mixing molar ratioof the lysine to the citric acid is from 1.7:1 to 1:3.
 5. The adhesivecomposition of claim 1, wherein a solid content of the adhesivecomposition is equal to or less than 70 parts by weight based on a totalweight of the adhesive composition.
 6. The adhesive composition of claim1, further comprising at least one solvent selected from a primaryalcohol, a polyhydric alcohol, a diol, and a triol.
 7. The adhesivecomposition of claim 6, wherein the alcohol comprises: at least onemonohydric alcohol selected from methanol, ethanol, propane-2-ol,butane-1-ol, pentane-1ol, and hexadecane-1-ol; at least one polyhydricalcohol selected from ethane-1,2-diol, propane-1,2-diol,propane-1,2,3-triol, butane-1,3-diol, butane-1,2,3,4-tetraol,pentane-1,2,3,4,5-pentol, hexane-1,2,3,4,5,6-hexol, andheptane-1,2,3,4,5,6,7-heptol; an unsaturated aliphatic alcohol selectedfrom prop-2-ene-1-ol, 3,7-dimethylocta-2,6-dien-1-ol, andprop-2-yn-1-ol; at least one alicyclic alcohol selected fromcyclohexane-1,2,3,4,5,6-hexol and 2-(2-propyl)-5-methylcyclohexane-1-ol;or a mixture thereof.
 8. The adhesive composition of claim 1, whereinprecipitates are not formed in the adhesive composition when stored at atemperature of −18° C. to 45° C. for 14 days or longer.
 9. The adhesivecomposition of claim 1, wherein a contact angle of the adhesivecomposition with a surface of a substrate to which the adhesivecomposition is applied is from 15° to 70°.
 10. A method of preparing anadhesive composition, the method comprising: mixing lysine, citric acid,and water to thereby form a mixture of the lysine, the citric acid, andthe water; and stirring the mixture at a temperature of 80° C. or less,wherein amounts of the lysine, the citric acid, and the water areadjusted such that precipitates of the lysine and the citric acid do notform in the adhesive composition.
 11. The method of claim 10, wherein amixing molar ratio of the lysine to the citric acid is from 1.7:1 to1:3.
 12. The method of claim 10, wherein the mixture further comprisesat least one solvent selected from a primary alcohol, a polyhydricalcohol, a diol, and a triol.
 13. An adhesive product comprising theadhesive composition of any one of claims 1 to 9.